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AUTHORS: David Lucchesi, South Dakota Game, Fish & Parks; Matthew Wagner, Mississippi Department of Wildlife, Fisheries, & Parks; Tanner Stevens, Minnesota Department of Natural Resources; Brian Graeb, South Dakota State University
ABSTRACT: The unauthorized introduction of flathead catfish (Pylodictis olivaris) into Lake Mitchell presented a unique opportunity to study the population dynamics of this species in a South Dakota impoundment. We collected flathead catfish using daytime low frequency electrofishing during nine sampling events from June 2013 through June 2015 to examine population characteristics including abundance, recruitment, mortality, growth, condition, and diet. We were most effective at collecting flathead catfish in the month of June, and catch per hour (CPUE) increased with the addition of a chase boat. The number of flathead catfish in Lake Mitchell was estimated at 1,348 individuals (95% CI = 459-1,455; density = 4.97/ha) in 2014 and 1,197 individuals (95% CI = 931-1,461; density = 4.42/ha) in 2015. Individuals from 12 year classes ranging from 1 to 13 years old were present. The population exhibited consistent recruitment, and annual mortality was estimated at 39%. Flathead catfish grew quickly exceeding stock length at age-3 and quality length at age-5; however, growth slowed in 2015. Similarly, condition of substock and stock-quality length fish declined in 2014 and 2015, respectively. The decline in growth and condition coincided with the recruitment of a large year class in 2012 and may be an early indicator of intraspecific competition. Diets of Lake Mitchell flathead catfish primarily consisted of crayfish (Orconectes spp.) and fish, mostly Centrarchidae. Based on our findings, we believe that the Lake Mitchell flathead catfish population is in its growth phase, possibly close to carrying capacity. Future studies are necessary to assess if this population will eventually experience a decline in growth and abundance similar to other introduced flathead catfish populations.
